1. Field of Invention
The present invention relates to a preparation method of a compound, and more particularly to a preparation method of carfentrazone-ethyl.
2. Description of Related Arts
The carfentrazone-ethyl, namely Ethyl 2-chloro-3-[2-chloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]-4-fluorophenyl]propionate whose molecular formula is C15H14Cl2F3N3O3, is a triazolinone herbicide having a following structure.

The carfentrazone-ethyl is conventionally prepared mainly by the following three methods: method one as disclosed in WO1990002120, CN1031307C and U.S. Pat. No. 5,125,958, wherein carfentrazone-ethyl is obtained via a diazotization of a 5-amino intermediate by the diazotization reagent of tert-butyl nitrite with molar quantities of copper chloride in the solvent of acetonitrile and a reaction with excess ethyl acrylate; method two as disclosed in WO1997007107, CN1068594 and U.S. Pat. No. 5,621,112, wherein carfentrazone-ethyl is obtained via a diazotization of the 5-amino intermediate hydrochloride in the aqueous solution of acetone having cuprous chloride as the catalyst and sodium nitrite as the diazotization reagent, and a simultaneous reaction with excess ethyl acrylate; and method three as disclosed in WO1999019308 and CN115301C, wherein the reaction between the 5-poition halogenated intermediate and the alkyl alkanoate in the presence of the palladium catalyst produces the alkyl propanoate having acetyl at the alpha-position which is chlorinated via sodium hypochlorite to obtain the object product, carfentrazone-ethyl.
Both method one and method two belong to Meerwein arylation and are related to diazotization reaction. As is known to those skilled in the art, diazotization reaction has many side reactions, such as thermal decomposition of diazonium salt, halogenations (Sandmeyer reaction), coupling, etc., which result in too many impurities making it difficult to obtain high quality product via the conventional purification method, since the object product is a viscous oil. Method three not only requires expensive palladium catalyst, but also suffers from the difficulty of purification.